Humidifier tub



FIG. 1 is a front perspective view of a humidifier tub for a respiratory apparatus according to our design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof; and,

FIG. 6 is a right side view thereof, with the left side view thereof being a mirror image thereof. 

The ornamental design for a humidifier tub, as shown and described. 